It's a stereotype that Mexicans wear sombreros and all have jobs mowing lawns. Stereotypes are SUPPOSED to be fallacious and false representations of entire groups. That's what makes them stereotypes. So in that sense, what the sorority portrayed WAS a true stereotype.

What the sorority probably meant to say is "We apologize for being jackasses" but thought it would be better if they could somehow add in all these formal and sincere words to help their cause. They just sucked at it, that's all.